Sam Jasenosky was surprised to learn that her fiancé didn't have to take his 2007 Toyota Prius in for an annual emissions inspection as he had in his home state of North Carolina before he moved here.

"I thought, 'Why don't we have to take this car in?,' " she recalled. "The way we are trying to tackle climate change, it would be a really good idea."

Jasenosky, 26, of South St. Paul, turned to Curious Minnesota, our community-driven reporting project, to find out why Minnesota doesn't require the tests.

Metro area motorists might remember when emissions tests were mandatory. From 1991 to 1999, drivers had to pay $8 to have their vehicles tested for carbon monoxide and other pollutants before renewing license tabs. The Minnesota Pollution Control Agency (MPCA) instituted the tests after the Environmental Protection Agency (EPA) in Washington, D.C., found carbon monoxide levels in the Twin Cities exceeded federal air quality standards and ordered the state to take action.

In the first month of testing in July 1991, about 20% of vehicles had tailpipe emissions that exceeded limits on hydrocarbons, carbon monoxide or both, said Rocky Sisk, a program administrator for the MPCA. But in the following years, fewer and fewer of the 1.2 million vehicles tested annually failed as older vehicles were taken off the road and replaced with newer ones with better technology. Cleaner fuel also helped bring down the failure rate, Sisk said.

Within eight years, carbon monoxide levels in the seven-county metro area were compliant with EPA standards, and the program was scrapped.

"It was always slated to end when we met carbon monoxide standards," Sisk said. "We put in a plan to reduce carbon monoxide. We reduced them and we didn't need it [the testing] anymore."

Aside from freeing up time by taking one task off motorists' to-do lists, eliminating the testing took away a roadblock for drivers who could not afford repairs. Drivers whose vehicles failed could get a one-year exemption if fixes cost more than $200, or $75 for vehicles made from 1976 to 1980. But they still had to get their vehicles repaired.

"There was a lot of grumbling in the Twin Cities," Sisk said. "It was not a popular program."

Across the country, 31 states plus the District of Columbia operate vehicle emission inspection and maintenance programs in at least one area of the state, said Maggie Sauer­hage, an EPA spokeswoman.

One of the largest is California, where ground-level ozone creates significant air pollution. Ozone, the main ingredient in smog, is formed when pollutants chemically react in the presence of sunlight. The state instituted its Smog Check Program in 1984 and has met air quality standards since, said Ben Doci, a spokesman for the California Bureau of Automotive Repair.

Twin Cities carbon monoxide levels have been in compliance with EPA standards for the past 20 years, and "I don't see us going back above them," Sisk said.